I have no direct knowledge about dark hulled Jeanneaus but in my experience with my own dark hulled boats, I found that the boat tended to get coated with salt as water flash dried on the topsides much easier than my white boats. This meant that I was scrubbing the hull more frequently and that the fenders were more likely to abrade the hull where the fenders rolled back and forth on the hull. As a result, I was waxing the hull three or four times a year to keep the boat looking bristol.

Although I believe that dark hulls are a lot more maintenance I just bought a boat with a dark blue hull. That said, at some point I intend to have the boat painted white.